The present invention relates to a sensor element for detecting a specific gas component in a gas under measurement and a sensor equipped with such an sensor element.
As an example of a sensor having a sensor element for detecting a specific gas component in a gas under measurement, conventionally known is an oxygen sensor for use in an exhaust system of an internal combustion engine to measure the concentration of oxygen in an exhaust gas for combustion control of the internal combustion engine. This oxygen sensor has, for example, a cylindrical metal shell and a plate-shaped sensor element held in the metal shell.
Japanese Laid-Open Patent Publication No. 2005-049115 (hereinafter abbreviated as “JP2005-049115A”) discloses one type of sensor element that includes a detection portion located on a front side in a longitudinal direction thereof and an air introduction portion adapted to introduce air thereinto. The detection portion has a measurement electrode exposed to a gas under measurement, a reference electrode arranged in the air introduction portion and a plate-shaped solid electrolyte member held in contact with both of the measurement electrode and the reference electrode. Upon contact of the gas under measurement with the measurement electrode and contact of the air with the reference electrode, the sensor element generates an electromotive force between the measurement electrode and the reference electrode via the solid electrolyte member according to a ratio between the concentrations of a specific gas component (oxygen) in the gas under measurement and in the air. The thus-generated electromotive force can be used as a gas detection signal for detection of the specific gas component.
The sensor element is shifted to an activated state capable of detecting the specific gas component when the solid electrolyte member is heated to an activation temperature by a heater. In particular, the sensor element of JP2005-049115A shows good gas responsivity, rapid temperature rise by the heater and high durability against repeated rapid temperature rises.